Apparatus for Upgrading Heavy Hydrocarbons Using Supercritical Water

ABSTRACT

Heavy hydrocarbons are upgraded more efficiently to lighter, more valuable, hydrocarbons with lower amounts of solid carbonaceous by-products in supercritical water using two heating stages, the first stage at a temperature up to about 775K and the second stage at a temperature from about 870K to about 1075K. The temperature is preferably raised from the first temperature to the second temperature by internal combustion using oxygen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of application Ser. No. 12/033,933 filed on Feb.20, 2008 which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to upgrading low value, heavyhydrocarbons, i.e. converting heavy hydrocarbons into more valuable,lower molecular weight (or “lighter”) hydrocarbons, using supercriticalwater (“SCW”).

Heavy hydrocarbons may be upgraded in partial oxidation processes.“Partial oxidation” refers generally to the combustion of a fuel using asub-stoichiometric amount of oxygen (“O₂”) to produce a “synthesis gas”(or “syngas”) comprising carbon monoxide and hydrogen. The synthesis gas(which also contains methane and carbon dioxide) can then be convertedinto light hydrocarbons in, for example, a Fisher-Tropsch process.

Broadly speaking, there are two types of partial oxidation process, i.e.thermal partial oxidation (“TPOX”) and catalytic partial oxidation(“CPOX”). Current TPOX processes generally require high temperatures,typically above 1600K, and high pressures, typically from 40 to 70 bar,and efficiency is rather low (e.g. 70% dry gas efficiency for aTexaco/GE quench gasifier and 80% for a Shell dry feed gasifier).Accordingly, there is a need to develop an alternative process to thecurrent TPOX process to improve the efficiency of upgrading heavy, lowvalue, hydrocarbons.

Molecular modeling studies carried out under the direction of theInventor predicted that partial oxidation of heavy hydrocarbons in SCWwith pure oxygen gas would be rapid at lower temperatures, e.g. from600K to 1000K, and pressures, e.g. 250 bar to 350 bar. Importantly,these studies predicted the same spectrum of products as produced inconventional TPOX reactions. Unexpectedly, experimental studies revealedthat, in contrast to the results predicted by the molecular modelingstudies, lower molecular weight hydrocarbon compounds are produceddirectly from reaction of heavy hydrocarbon feedstock in SCW.

SCW is already known to a certain extent for use in processes to converthydrocarbon compounds. For example, it has been reported (“Pyrolysis ofeicosane in supercritical water”; Vostrikov et al Russian ChemicalBulletin, Int Ed.; Vol. 50, No. 8, pp. 1478-1480, August 2001) thateicosane can be converted into a mixture of methane, carbon monoxide,carbon dioxide and hydrogen by heating in SCW at 30 MPa (300 bar) and ata temperature from 450° C. to 750° C. (˜723K to ˜1023K). It has alsobeen reported (“Naphthalene oxidation in supercritical water”; Vostrikovet al; Russian Chemical Bulletin, Int. Ed.; Vol. 50, No. 8, pp.1481-1484, August 2001) that naphthalene can be converted into a mixtureof benzene, toluene, methane, hydrogen, soot and carbon oxides byheating in SCW at 30 MPa (300 bar) and at temperature from 660° C. to750° C. (˜935K to ˜1025K).

U.S. Pat. No. 4,421,631 (Ampaya et al; published in 1983) discloses aprocess for upgrading a heavy hydrocarbon material, e.g. a petroleumresidual, using a molten salt, e.g. alkali metal carbonate(s). Heat forthe process is provided by combustion of carbonaceous material, producedas a by product of the upgrading process and entrained in the flow ofmolten salt, using oxygen.

Processes to upgrade low value, heavy hydrocarbons into more valuable,lighter hydrocarbons using water under supercritical conditions are alsoknown.

U.S. Pat. No. 1,956,603 (White; published in 1934) discloses “aquolysis”processes for converting heavy petroleum hydrocarbons including tars,tarry oils and shale oil into liquids of lower boiling points by heatingthe heavy hydrocarbons in the form of an emulsion with water at atemperature from 900° F. to 1300° F. (˜755K to ˜980K) and a pressurefrom below 100 bar to above 1000 bar. It is disclosed that supercriticalpressures are preferred.

U.S. Pat. No. 3,989,618 (McCollum et al; published in 1976) discloses aprocess for upgrading hydrocarbons including heavy materials such as gasoil, residual oils, tar sands oil, oil shale kerogen extracts andliquefied coal products by contacting the hydrocarbons with awater-containing fluid at a temperature in the range of 600° F. to 900°F. (˜590K to ˜755K) and, preferably, at about 705° F. (647K) which isthe critical temperature of water. U.S. Pat. No. 3,989,618 exemplifiesheating tar sands oil in water (1:3) at a temperature of 752° F. (˜675K)and at a reaction pressure of 4350 psig (˜300 bar) for 3 hours in anautoclave. The tar sands oil was cracked to produce hydrogen, carbondioxide and methane gases (11.2 wt % total), light ends (75.2 wt %),heavy ends (8.6 wt %) and a solid residue (5.0 wt %). U.S. Pat. No.3,989,618 also exemplifies semi-continuous flow processing of tar sandsoil in water (1:3) at 752° F. (˜675K) and 4100 psig (˜285 bar) in anexternally-heated pipe reactor having a reaction volume of about 6milliliters.

U.S. Pat. No. 4,840,725 (Paspek; published in 1989) discloses a processfor converting heavy hydrocarbon oil feedstocks to fuel range liquids.The process involves contacting the heavy hydrocarbons with water(typically, 2:1 to 1:1) at a temperature from 600° F. to 875° F. (˜590Kto ˜740K) at a pressure preferably from 4000 psi to 6000 psi (˜275 barto ˜415 bar). It is disclosed that reaction times are generally short(from a few seconds up to about 6 hours) and that the fuel range liquidsproduced have increased amounts of high value aromatic carbons. U.S.Pat. No. 4,840,725 exemplifies converting shale oil using a 400 mlvertical tube reactor operating at 825° F. (˜715K) and 4900 psi (˜340bar). U.S. Pat. No. 4,840,725 acknowledges that coke is produced as a byproduct of the reaction of feedstock with SCW and indicates that thereaction temperature should not exceed 875° F. (˜740K) in order tominimize formation of this by product.

U.S. Pat. No. 4,818,370 (Gregoli et al, published in 1989) disclosesprocesses for upgrading heavy hydrocarbons using brine undersupercritical conditions. It is disclosed that hydrocarbon deposits maybe upgraded in situ in subterranean reservoirs and that heat for theseprocesses may be provided by pumping oxygen into the reservoir tocombust a portion of the deposits. Temperatures in the combustion zoneare allowed to reach ˜478K to ˜1030K at which point the combustion isstopped to allow heat to soak through the reservoir and for theupgrading reactions to occur.

US 2005/0040081 (Takahashi et al, published in 2005) discloses a processfor upgrading heavy hydrocarbon oil using SCW at a temperature up to˜725K to produce lighter hydrocarbons which are combusted in a gasturbine to generate power. Any unreacted hydrocarbon residue iscombusted to produce heat which is used, together with heat produced inthe gas turbine, to heat water for the process. Further heat for thecracking process is provided externally using a heater. However, it isdisclosed that the amount of heat supplied externally may be reduced byreacting a portion of the heavy hydrocarbon with an oxidant.

US 2007/0144941 (Hokari et ah, published in June 2007) discloses aprocess for upgrading heavy hydrocarbon oil using SCW in the presence ofan oxidant, e.g. oxygen, to remove vanadium from the heavy oil to ensurethat vanadium is not present in the lighter hydrocarbon products.

There is a need for new processes for upgrading heavy hydrocarbonfeedstock. New direct conversion processes should be more efficient thanexisting processes, for example by increasing the overall yield of thelighter hydrocarbons and by improving the spectrum and distribution ofhydrocarbons produced. In addition, new processes should improve controlof the formation of unwanted solid carbonaceous by-products such as cokeand soot.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda process for converting heavy hydrocarbon feedstock into conversionproducts comprising lower molecular weight hydrocarbon compounds, saidprocess comprising:

-   -   mixing heavy hydrocarbon feedstock and supercritical water        (“SCW”) to form a fluid reaction mixture at a first temperature        up to about 775K;    -   heating said fluid reaction mixture to a second temperature from        about 870K to about 1075K;    -   maintaining said fluid reaction mixture at said second        temperature for sufficient time to form a resultant fluid        mixture containing said conversion products.

In the context of the present invention, “heavy hydrocarbon feedstock”is hydrocarbonaceous materials typically having an initial boiling point(“IBP”) of at least 300° C. (˜575K), preferably at least 400° C.(˜675K), and most preferably at least 500° C. (˜775K). The feedstock isusually characterized by the presence of polycyclic aromatichydrocarbons such as asphaltenes. The feedstock may be heavy residualby-products of oil refining or may be naturally occurring materials.Examples of suitable heavy hydrocarbons for use with the presentinvention include bitumen (or asphalt); pitch; tar; tar sand oil; vacuumresidue; shale oil; kerogen; and coal tar. The invention has particularapplication to the conversion of bitumen, pitch or tar.

“Lower molecular weight hydrocarbon compounds” are hydrocarbon compoundshaving a lower molecular weight than the heavy hydrocarbon feedstock.The lower molecular weight hydrocarbon products have lower viscositiesand lower boiling points than the heavy hydrocarbon feedstock.

The lower molecular weight hydrocarbon compounds are typically producedin three fractions, i.e. a gas fraction; a liquid hydrocarbon fractionhaving a density less than water; and a hydrocarbon fraction having adensity greater than water. The gas fraction usually comprises C₁-C₄alkanes such as methane, ethane and propane; and C₂-C₄ alkenes such asethene and propene. The gas fraction typically also includes hydrogen;carbon monoxide; and carbon dioxide. The liquid hydrocarbon fractionusually comprises a mixture of benzene; toluene; and xylenes (“BTX”).The denser hydrocarbon fraction usually comprises the heavier, e.g.C₈-C₂₀ hydrocarbon fragments. Solid carbonaceous materials such as coke,soot and/or carbon are also produced.

“SCW” is water which is at a temperature and pressure exceeding itscritical temperature and critical pressure. The critical temperature ofwater is the temperature above which water cannot be liquefied by anincrease in pressure, i.e. 374° C. (647K). The critical pressure ofwater is the pressure of water at its critical temperature, i.e. 22.1MPa (221 bar).

According to a second aspect of the present invention, there is provideda reactor system for converting heavy hydrocarbon feedstock intoconversion products comprising lower molecular weight hydrocarboncompounds, said reactor system comprising:

-   -   a source of SCW;    -   a mixing zone for mixing heavy hydrocarbon feedstock and SCW to        form a fluid reaction mixture at a first temperature up to about        775K;    -   a feeding system for feeding SCW from said source and feedstock        into said mixing zone;    -   a heating system for heating said fluid reaction mixture from        said first temperature to a second temperature from about 870K        to about 1075K;    -   a higher temperature reaction zone for maintaining said fluid        reaction mixture at said second temperature for sufficient time        to form a resultant fluid mixture containing said conversion        products, said reaction zone being in fluid flow communication        with said mixing zone; and    -   an outlet system for removing said resultant fluid mixture.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross sectional representation of a first embodiment of thereactor according to the present invention; and

FIG. 2 is a schematic representation of an embodiment of the processaccording to the present invention involving a second embodiment of thereactor.

DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention comprises mixing SCW and, typicallypre-heated, feedstock to form a fluid reaction mixture at a firsttemperature up to about 775K. The fluid reaction mixture is thought tobe a single phase, homogeneous mixture. The fluid reaction mixture isheated to a second temperature from about 870K to about 1075K andmaintained at said second temperature for sufficient time to produce aresultant fluid mixture containing said lower molecular weighthydrocarbon compounds and, typically, solid carbonaceous material. Solidcarbonaceous material may have been deposited on the surface of internalcomponents of a reactor in which the process takes place.

The feedstock is usually warmed to a suitable temperature to reduceviscosity so that the feedstock can be pumped to the required pressure.The Inventor has observed, however, that bitumen cakes (i.e. viscosityactually increases due to polymerization) at temperatures above about725K. Thus, heavy hydrocarbon feedstock is usually pre-heated to atemperature below the upper solidification temperature of the feedstock.The upper solidification temperature varies between different feedstocksand the temperature of the pre-heated feedstock will depend on thebehavior of the actual feedstock used. However, feedstock is preferablyat a temperature of no more than 725K, e.g. from about 647K to about725K. Such a temperature is particularly suitable if the feedstock isbitumen.

The temperature of the SCW is typically selected to ensure that thetemperature of the fluid reaction mixture is from about 650K to about775K after the feedstock is mixed with the SCW. Before mixing with thefeedstock, the SCW is usually at a temperature from about 650K to about900K.

Provided that the pressure of the process is over the critical pressureof water (about 22.1 MPa or 221 bar), the pressure is not critical tothe invention. The pressure may be up to about 100 MPa (1000 bar), e.g.up to about 50 MPa (500 bar). The pressure is preferably from about 25MPa to about 40 MPa (250 bar to 400 bar), e.g. about 30 MPa (300 bar),as such pressures ensure the presence of supercritical conditions forthe mixture of water and hydrocarbons in the system.

The mass ratio of feedstock to water is typically from about 2:1 toabout 1:10, usually from about 3:2 to about 1:6 and, typically, fromabout 1:1 to 1:2.

Experimental investigations have determined that a preferred value forthe first temperature is typically from the supercritical temperature ofwater, i.e. about 647K, to about 775K, and preferably from about 650K toabout 755K, e.g. about 675K to about 725K, and that the secondtemperature is preferably from about 925K to about 1050K and morepreferably from about 950K to about 1025K.

Without wishing to be bound by any particular theory, the twooperational ranges of temperature are chosen corresponding to twopossible mechanisms of reaction. The first temperature range istypically about 647K to about 775K. In this range, the heavy hydrocarbonfeedstock forms primarily a single phase, homogenous mixture with SCWwith a minor amount of undissolved residue having a high carbon tohydrogen ratio which also contains the ash and at least the bulk of theinorganic content of the feed. Feedstock molecules are understood tobreak down under these conditions to produce lighter hydrocarbonfragments, having a higher hydrogen to carbon ratio than the feedstock,and leaving a higher carbon to hydrogen ratio fraction as a non-reactiveinsoluble residue. At the first temperature, the water is acting as asolvent and as a heat carrier but does not actually react with thefeedstock itself.

Preliminary investigations regarding the first stage used experimentsinvolving injecting pre-heated tar (vacuum residue having compositionC₁H_(1.43)S_(0.015)) into SCW within a horizontal reactor with aconstant wall temperature of about 690K at a pressure of about 300 bar.The investigations revealed that the tar dissolved in the SCW bydiffusion alone until an equilibrium point was reached in about 75minutes. About 76% of the total tar mass was recovered as useful lighterhydrocarbon products in three distinct fractions, leaving about 24% ascoke having a carbon to hydrogen ratio of about 1:1.13. The threefractions were:

(a) a gas fraction (29.9% of the total tar mass) having a composition asfollows:

-   -   CH₄ 47.6% (molar);    -   C₂H₆ 29%;    -   C₃H₆ 13.3%;    -   C₂H₆ 3.4%;    -   C₃H₈ 6.0%; and    -   C₃₊ 0.7%,        (b) a hydrocarbon fraction having a density less than water        (33.7% of the total tar mass) with about half of the fraction        having a boiling point of less than 373K; and        (c) a “heavy” hydrocarbon fraction having a density greater than        water (heating this fraction to 723K in a vacuum loses 22.7% of        mass evaporated; extraction with toluene left a final residue of        24% of the total tar mass).

Analysis of the total liquid fraction [(b) plus (c)] showed that thetotal mass fraction of hydrocarbon molecules, with carbon atom numbersof 12 or less, was 36% while the total mass fraction with a boilingtemperature of less than 573K was 42%.

The Inventor observed that sulfur present in the tar is released partlyas H₂S and partly as COS and a good deal is retained in the residualcoke. The degree of release of sulfur as H₂S and COS was seen toincrease as the temperature was raised. During a test at 300 bar in ahorizontal reactor at 690K for duration of 2 hours and with no mixingexcept diffusion, the total mass proportion of sulfur in the tar feedreleased as H₂S was 27.3%. This proportion will be maintained for lowerresidence times with increased mixing of the tar and supercriticalwater.

Rapid mixing of the feedstock and the SCW is, however, preferred. Thetime taken to reach mixing equilibrium is drastically reduced byagitating the mixture by creating flow turbulence. Flow turbulence maybe created by a device such as a static mixer or otherwise by anarrangement of concentric shells defining a convoluted path or“multi-pass” arrangement. The use of a high flow velocity also createsflow turbulence. The time required to form the fluid reaction mixturecan be reduced by increasing the temperature of the solution up to about775K although it is important to bear in mind the upper solidificationtemperature of the feedstock. The feedstock is preferably atomized, e.g.using a suitable high intensity nozzle mixer, to increase interfacialsurface area between feedstock and SCW.

In preferred embodiments, the period of time over which the feedstock ismixed with SCW is typically from about 1 second to about 10 minutes.This period is preferably less than 5 minutes and, more preferably, fromabout 5 seconds to about 60 seconds.

The second mechanism of reaction occurs in the range of the secondtemperature, i.e. from about 870K to about 1075K. The Inventor believesthat, at the second temperature, water reacts with hydrocarbon moleculesin accordance with the following equation:

(n+4)C+2nH₂O—→4→CH_(n) +nCO₂

(where the feed C refers to carbon in high molecular weighthydrocarbons) thereby hydrogenating feedstock fragments and increasingthe yield of lighter, more valuable, hydrocarbon products and improvingthe distribution of products. The rate of conversion is determined bythe kinetics of essentially gas phase reactions. The hydrogenationreactions are understood to be substantially isothermal. At this stage,not only is SCW acting as a solvent and a heat carrier, it is alsoacting as a hydrogenator.

Once the temperature rise has occurred, it is necessary to maintain thefluid reaction mixture at the second temperature for sufficient time toallow not only the free-radical reactions but also the hydrogenationreactions to occur, which leads to formation of valuable products withhigher hydrogen to carbon ratio than the feedstock. The period of timeover which the fluid reaction mixture is maintained at the secondtemperature is typically from about 1 second to about 10 minutes. Inpreferred embodiments, this period is less than 5 minutes and,preferably, from about 5 seconds to about 60 seconds.

The period to form the fluid reaction mixture is, typically, longer thanthe period at which the mixture is maintained at the second temperature.Ultimately, the difference in the two periods depends on the particularconversion in question. However, a ratio of the periods from about 2:1to about 4:1 may be appropriate.

The Inventor has observed that reaction temperatures between the upperlimit of the first temperature range and the lower limit of the secondtemperature range (e.g. from about 775K to about 870K) unfortunatelyfavor bitumen caking and formation of solid carbonaceous material suchas hard coke and fluffy carbon soot rather than the formation of thedesired conversion products. Neither of these effects is desirable asthey both lead to loss of recovery and increased risk of blockage of thereactor and associated apparatus, necessitating the reactor being takenoff-line for periodic cleaning. Therefore, in order to reduce the numberof times the reactor needs to be cleaned, the solution is preferablyheated from the first temperature to the second temperature as fast aspossible, i.e. in as short a time as possible, to avoid undue formationof unwanted solid carbonaceous deposits. In preferred embodiments, thefluid reaction mixture is heated from the first temperature to thesecond temperature in no more than 20 seconds, preferably in no morethan 10 seconds, more preferably in no more than 5 seconds and mostpreferably in less than 1 second.

The soot and coke formation occurs by dehydrogenation of the feedstockdown to an approximate formula CH_(0.5). The dissociation of watermolecules has been shown to become significant at a temperature of over925K. It appears that above this temperature the soot potential radicalsare oxidized in reactions such as:

2CH_(0.5)+2H₂O→2CO+2H₂+H

Thus, one molecule of water should be required for each mol of CH_(0.5)radical. It has also been found, experimentally, that the rate of thisreaction is greater than the rate of formation of CH_(0.5) and free Cradicals at these temperatures, so that the soot suppression at above925K takes place with less than an overall 2:1 water ratio.

At least a portion of the heat required to increase the temperature ofthe solution from the first temperature to the second temperature may beprovided externally, e.g. from a furnace or by electrical heatingelements. However, in preferred embodiments, at least a portion and,preferably all, of the heat required to heat the fluid reaction mixturefrom the first temperature to the second temperature is providedinternally.

The fluid reaction mixture will typically comprise combustiblecomponents including hydrocarbonaceous components (e.g. selected fromfeedstock and/or lower molecular weight hydrocarbon compounds andfragments) and carbonaceous components (e.g. selected from coke, sootand/or carbon). The addition of gaseous oxygen (O₂) to the fluidreaction mixture results in combustion of a portion of these combustiblecomponents.

The portion of the combustible components that react with oxygen toincrease the temperature from the first temperature to the secondtemperature usually equates to no more than 30 wt %, preferably no morethan 20 wt %, e.g. from about 10 wt % to about 20 wt % of the feedstock,particularly in embodiments in which the feedstock is bitumen.

An oxygen-containing gas such as air may be introduced to combust theportion of combustible components. However, an oxygen-containing gascontaining at least 50%, preferably at least 90%, and more preferably atleast 95%, oxygen (with the remainder being an inert carrier gas such asnitrogen) is typically used. The use of “pure” oxygen, i.e. at least 99%oxygen, is preferred.

The oxygen-containing gas is preferably pre-heated to a suitabletemperature which is typically from about 550K to about 700K, preferablyfrom about 600K to about 650K, e.g. about 625K. The oxygen-containinggas will be introduced to the fluid reaction mixture at the operatingpressure of the process.

The temperature of the second stage of the reactor is carefullycontrolled by the amount of oxygen-containing gas added to the fluidreaction mixture. The amount of oxygen is a control variable for theprocess and is defined by the heat balance. In this connection, it iswell within the ability of the skilled person to calculate the requiredamounts of oxygen necessary to control the temperature of the secondstage as required based on the mass flows rates of SCW and feedstock(hence, the composition of the fluid reaction mixture), the requiredmixing temperature and the temperature of the oxygen.

The upper and lower limits of the amount of oxygen used may be definedempirically based on the highest and lowest hydrocarbon to water massratios and the highest and lowest temperature rises from the firsttemperature to the second temperature. For example, an appropriate totalamount of oxygen gas for a process converting bitumen at a mass ratiowith water of 1:1 to 1:2 with a temperature rise from the firsttemperature to the second temperature from about 95K to about 428K istypically about 15 wt % to about 60 wt %. These figures may, of course,refer to the total amount of pure oxygen or the total amount of oxygenfed as a component in an oxygen-containing gas.

The Inventor has observed that the exothermic reaction causes anextremely rapid temperature rise. The presence of water moderates thetemperature rise, and the very rapid reaction, which typically takesplace in well under 1 second, does not lead to any significant sootformation.

An important feature of the stage of the process at the secondtemperature is the hydrocracking reaction with hydrogen derived fromreaction between water molecules and the hydrocarbon material. Thisreaction may be improved by feeding hydrogen gas to the fluid reactionmixture at the second temperature to assist with the hydrogenation ofthe hydrocarbon material.

The hydrogen gas may come from an external source. Alternatively, thehydrogen could be produced by gasifying residual hydrocarbon material orby partial oxidation of coke, e.g. coke produced in the process. If theresidual bitumen is gasified using pure gaseous oxygen in a conventionalgasifier with carbon dioxide capture producing hydrogen which is thenused to hydrogenate the fluid reaction mixture, the nett coke productionmay be dramatically reduced and both the yield and hydrogen to carbonratio of the product slate may be improved.

The process is carried out in a reactor system. A suitable reactorsystem is a batch reactor such as an autoclave. However, in preferredembodiments, the process is carried out in a continuous flow reactor.The process preferably has a total residence time within a continuousflow reactor from about 2 seconds to about 20 minutes, e.g. from about 5seconds to about 10 minutes, preferably about 10 seconds to about 5minutes.

In embodiments where the reactor system has a mixing zone, the residencetime in the mixing zone may be from about 1 second to 10 minutes, e.g.from about 5 seconds to about 60 seconds and, preferably about 30seconds. In embodiments where the reactor system has a highertemperature reaction zone, the residence time in the reaction zone maybe from about 1 second to about 10 minutes, e.g. from about 5 seconds toabout 60 seconds and, preferably about 30 seconds.

The reactor system will usually be operated in a discontinuous or cyclicmanner comprising an “on-line” phase (when feedstock is fed to thereactor system and converted into the conversion products), followed byan “off-line” phase in which only SCW and an oxygen-containing gas enterthe reactor system to burn off solid carbonaceous deposits.

The reactor system typically operates in the “on-line” phase until theextent of the deposition of solid carbonaceous material is such that thereactor system needs to be cleaned. The period of the “on-line” phase ishighly variable and depends on several factors such as the compositionof the feedstock and the material from which the internal components ofthe reactor (e.g. those components in contact with the fluid reactionmixture) are made. The period may be from as little as about 30 minutesto as much as about 1 week or more.

The reactor system typically operates in the “off-line” phase until thereactor system has been cleaned of the deposits of solid carbonaceousmaterial. The period of the “off-line” phase is highly variable anddepends on several factors such as the extent of the deposition and thematerial of the internal components. However, the “off-line” phaseusually lasts from about 5 minutes to about 1 hour.

The resultant fluid mixture may be supercritical or subcritical due tothe production of gaseous conversion products. The resultant fluidmixture usually comprises particles of solid material such as coke, sootand ash, entrained within the flow of the fluid. These particles arepreferably separated from the fluid. A suitable separator is ahydrocyclone device, e.g. a Norway-type entrainment separator, which maybe located in the base of the higher temperature reaction zone of thereactor system.

The resultant fluid mixture, typically with the solid particles removed,is usually cooled to near ambient temperature (such as from about 5° C.to about 65° C., e.g. about 20° C. to about 55° C. or about 35° C. toabout 50° C.) and the pressure reduced to allow liquid and vapor phasesto separate. The final pressure is usually chosen to facilitate theoptimum economics for separation of lower molecular weight hydrocarboncompounds, hydrogen, methane, etc. from the water phase. An appropriatefinal pressure may, for example, be from about 10 bar to about 100 bar,perhaps about 40 bar to about 60 bar, e.g. about 50 bar.

The water phase is usually recycled back to the process, typically withfresh make-up water.

Water, pressurized to the operating pressure of the process, may beheated by indirect heat exchange against the resultant fluid mixture ora fluid mixture derived therefrom, e.g. following removal of theentrained solid materials, to produce the SCW. However, the heatgenerated in the process is typically more than enough to produce theSCW. Accordingly, the process may comprise a steam heating cycle toprovide heat balance in which water is heated by indirect heat exchangeagainst the resultant fluid mixture, preferably following removal ofsaid entrained solid materials to produce steam. In these embodiments,at least a portion of the excess heat is used to heat water at apressure from about 100 bar to about 200 bar, e.g. 150 bar, to producesuperheated steam at a temperature of about 750K to about 850K, e.g.about 793K.

At least a portion of the steam may be used to pre-heat feedstock byindirect heat exchange. In embodiments in which oxygen is fed to thefluid reaction mixture to combust a portion of the combustiblecomponents of said fluid reaction mixture, at least a portion of thesteam may be used to pre-heat an oxygen-containing gas by indirect heatexchange. At least a portion of the steam may be used to generate powerin a steam turbine.

In preferred embodiments, a first portion of the steam is used topre-heat feedstock; a second portion of the steam is used to pre-heatthe oxygen-containing gas; and a third portion of the steam is used togenerate power is a steam turbine. The resultant water streams may becombined and recycled to a condensate pump for re-pressurization.

The hydrogenation process may be catalyzed using either a homogeneouscatalyst or a heterogeneous catalyst. Any suitable conventionalcatalysts may be used, including nickel-based catalysts. However, inpreferred embodiments, the process is uncatalyzed which is advantageoussince there is no catalyst to have to clean periodically or remove fromthe residual fluid mixture. The Inventor notes that bitumen oftencontains nickel and vanadium that may self-catalyze the hydrogenationreaction.

Limestone (CaCO₃), sodium carbonate (Na₂CO₃), or sodium hydroxide (NaOH)or mixtures thereof may be added to the feedstock to facilitatedesulfurization of the heavy hydrocarbon feedstock.

The reactor system comprises:

-   -   a source of SCW;    -   a mixing zone for mixing heavy hydrocarbon feedstock and SCW to        form a fluid reaction mixture at a first temperature up to about        775K;    -   a feeding system for feeding SCW from said source and feedstock        into said mixing zone;    -   a heating system for heating said fluid reaction mixture from        said first temperature to a second temperature from about 870K        to about 1075K;    -   a higher temperature reaction zone for maintaining said fluid        reaction mixture at said second temperature for sufficient time        to form a resultant fluid mixture containing said conversion        products, said reaction zone being in fluid flow communication        with said mixing zone; and    -   an outlet system for removing said resultant fluid mixture.

The reactor system typically comprises a source of feedstock. In suchembodiments, the feed system preferably feeds feedstock from thefeedstock source to the mixing zone.

A preferred continuous flow reactor is a tubular device with a highlength to diameter ratio. Such an aspect ratio reduces the capital costof the reactor as the reactor can have a thinner reactor wall. Inaddition, such an aspect ratio not only increases the length of theinternal flow path and but also the fluid velocities, thereby increasingfluid turbulence and promoting good mixing. An example of a suitablereactor might be a pipe reactor.

The feeding system preferably comprises an atomizer, such as a highintensity atomizing nozzle, for atomizing said feedstock at the point ofmixing with the SCW. The use of an atomizer increases the interfacialsurface area of the feedstock thereby facilitating formation of thefluid reaction mixture.

The reactor system usually comprises a device provided in the mixingzone to create flow turbulence. The turbulence created by such a devicefacilitates dissolution of the feedstock in the SCW and decreases thenecessary residence time of the mixture in the mixing zone. The devicemay be a static mixer or a set of internal concentric flow separationshells. For example, two internal concentric shells would provide a“three pass” arrangement and, with a constant area in each pass, wouldgive three times the flow velocity with the same residence time in areactor of a given volume. Such an arrangement reduces the walltemperature gradient and increases turbulence in the mixing zone of thereactor system.

The heating system may comprise an external heating system such as afurnace or an electrical heater. However, in preferred embodiments, theheating system is for providing heat internally within the reactorsystem.

The rise in temperature from the first temperature to the secondtemperature may be achieved by injecting an oxygen-containing gas intothe fluid reaction mixture. In these embodiments, the heating systempreferably comprises an oxygen inlet system for feedingoxygen-containing gas into said fluid reaction mixture.

The oxygen inlet system preferably provides a rapid, even reaction ofoxygen with the fluid reaction mixture. Such a reaction may be achievedby the introduction of the oxygen-containing gas into the fluid reactionmixture in either a single stage or in a plurality of stages. Eitherway, the oxygen inlet system preferably provides uniform injection ofthe oxygen-containing gas into the fluid reaction mixture.

The oxygen inlet system preferably comprises a device for creatingturbulence in a flow of fluid reaction mixture for facilitating mixingof oxygen with the fluid reaction mixture. In some embodiments, theoxygen-containing gas may be introduced to the fluid reaction mixturevia an atomizing mixing nozzle. In other embodiments, theoxygen-containing gas may be introduced to the fluid reaction mixturefrom under the periphery of at least one umbrella (where high fluidvelocities and turbulences exist) or stage-wise from under theperipheries of a plurality of umbrellas, typically arranged in series.

The oxygen-containing gas may come from any suitable location. Forexample, oxygen gas may be stored in a pressurized storage vessel andfed, with compression and/or pre-heating as required, to the oxygeninlet system of the reactor. Oxygen may be stored in a cryogenic storagetank as liquid oxygen; pumped in a LOX pump to the required pressure andheated in a suitable heat exchanger to produce oxygen gas at therequired temperature and pressure which is then fed to the oxygen inletsystem of the reactor system. However, in preferred embodiments, oxygenis produced on site in a cryogenic air distillation system, preferablyoperating a pumped LOX cycle. The LOX may taken from the cryogenicdistillation system, pumped to the required pressure and heated toproduce oxygen gas at the required temperature which is them fed to theoxygen inlet system of the reactor system.

The outlet system preferably comprises a separator for separatingentrained solid materials from the resultant fluid mixture. A suitableseparator is a hydrocyclone separator such as a Norway-type entrainmentseparator. The separator may be located outside the higher temperaturereaction zone of the reactor system. However, in a preferred embodiment,the separator is located within the higher temperature reactor system,e.g. in the base thereof.

The Inventor has observed that there is a large amount of deposition ofsolid carbonaceous material in reactor systems having internalcomponents made from stainless steel and he has concluded that thecarbonaceous by-products are interacting with carbides in the steel.Therefore, in preferred embodiments, the internal components of thereactor system, i.e. those components in contact with the fluid reactionmixture, are made from a metal selected from the group consisting oftitanium and copper and alloys thereof.

In embodiments where all fluids in the product heat exchange system areclean and free from solid particles, the heat exchangers can befabricated as diffusion bonded multichannel blocks. Suitable heatexchangers would be those exchangers manufactured by Heatric Ltd (Poole,Dorset, UK) which are capable of achieving the required high temperatureand pressure and can be fabricated in corrosion resistant materials.

Provision is preferably made for oxygen dissolved in SCW at temperaturesabove 700K to be pumped into both the mixing and higher temperaturereaction zones of the reactor so that any deposits of coke and soot canbe removed by oxidation to carbon dioxide and water. In preferredembodiments, oxygen is added to the SCW and then fed to the reactor.

Referring to FIG. 1, tubular reactor 110 comprises a mixing zone 112 fordissolving heavy hydrocarbon feedstock in SCW to form a fluid reactionmixture at a temperature from 650K to 775K and a higher temperaturereaction zone 114 for heating the fluid reaction mixture at atemperature of 870K to 1075K for sufficient time to produce theresultant fluid mixture. The reaction zone 114 is in fluid flowcommunication with the mixing zone 112.

A stream 116 of pre-heated heavy hydrocarbon feedstock and a stream 118of SCW are combined in a feed system 120 and fed to the mixing zone 112.The mixing zone 112 comprises a static mixer 122 which mixes thefeedstock with the SCW to produce the fluid reaction mixture which flowsinto the reaction zone 114 which comprises an oxygen inlet system 124for feeding a stream 126 of oxygen into the fluid reaction mixturedownstream of the mixing zone 112. The oxygen inlet system 124 comprisesa series of three umbrellas 128, 130, 132 provided co-axially with thelongitudinal axis of the reactor 110. Oxygen is injected into thereactor from under the umbrellas to combust a portion of the feedstockin the fluid reaction mixture, thereby raising the temperature of thefluid reaction mixture from the first temperature to the secondtemperature. The umbrellas cause turbulence in the flow of fluidreaction mixture through the second zone thereby facilitating mixing ofthe oxygen with the mixture from under the annular periphery of theumbrellas.

The reactor 110 has an outlet 134 for removing the resultant fluidmixture as stream 136. Temperature sensors 138 and 140 monitor thetemperature within the reactor in both the mixing and higher temperaturereaction zones.

Referring to FIG. 2, reactor 210 has a mixing zone 212 and a highertemperature reaction zone 214. Feedstock, in this case bitumen, iswarmed to reduce its viscosity and produce a stream 216 of warmedbitumen. Stream 216 is pumped to 300 bar in pump 218 to produce a stream220 of pumped bitumen which is then pre-heated by indirect heat exchangein heat exchanger 222 against a condensing stream 224 of steam toproduce a stream 226 of pressurized and heated bitumen. The bitumen isheated to a temperature from about 650K to about 725K to avoid caking.The actual temperature of the pre-heated bitumen depends in part on theupper solidification temperature of the bitumen. Stream 226 is then fedto the reactor 210 via feed system 228.

A water stream 230, comprising a stream 232 of recycled water and astream 234 of make-up water, is pumped to 300 bar in pump 236 to producea stream 238 of pumped water. Stream 238 is heated by indirect heatexchange in heat exchanger 240 to produce a stream 242 of SCW at atemperature such that, when mixed with stream 226 of heated bitumen toproduce a fluid reaction mixture, the fluid reaction mixture is at afirst temperature from about 647K to about 775K.

Feed system 228 comprises a high intensity atomizing nozzle (not shown)for atomizing the heated bitumen into the SCW to facilitate dissolutionof the bitumen in the water. The mass ratio of bitumen to water is fromabout 1:1 to about 1:2.

The mixing zone 212 comprises two concentric shells defining a “threepass” arrangement of sections to increase the fluid velocity of themixture through the mixing zone 212. The SCW and bitumen mixture passesthrough the three concentric sections, taking about 30 seconds which issufficient time to allow the initial reduction in bitumen viscosity andthe initial cracking of the complex molecular structure of the bitumento take place. Most of the bitumen forms a single homogeneous phase withthe SCW (the fluid reaction mixture) but a small fraction of a solidphase, composed of ash and a residue having high carbon to hydrogenratio, is also formed.

The fluid reaction mixture leaves the mixing zone 212 via a mixingnozzle 244 where a stream 246 of pre-heated oxygen gas is introduced. Inthe exemplified embodiment, oxygen is separated from air in a cryogenicair separation plant 248 operating a pumped oxygen cycle producing astream 250 of pressurized oxygen product at the operating pressure ofthe reactor 210 (about 300 bar) which is pre-heated to about 625K byindirect heat exchange in heat exchanger 252 against a condensing stream254 of steam at 150 bar to produce the stream 246 of pre-heated oxygengas.

The oxygen reacts rapidly, e.g. within 1 or 2 seconds, with combustiblecomponents of the fluid reaction mixture and raises the temperature ofthe solution to a second temperature from about 870K to about 1075K,e.g. about 975K. The quantity of oxygen is derived from the flow ratesof the feedstock and the SCW and from the required first temperature. Inthe present example, the quantity of oxygen is about 30 wt % of that ofthe feedstock and the effect of which is that about 17 wt % of thehydrocarbon content of the fluid reaction mixture is combusted to raisethe temperature. The oxygen reacts with this portion of the hydrocarboncontent which is oxidized to carbon dioxide and water. The increase intemperature of the fluid reaction mixture causes free radical reactionsto take place which allow water molecules to react with the feedstockmolecules causing cracking and hydrogenation of the fragments withproduction of carbon dioxide. Residence time in the reaction zone isabout 10 seconds, producing the resultant fluid mixture. The increase intemperature following oxygen injection will result in a three foldreduction in fluid density.

There is no need to use internal baffles in the reaction zone 214 of thereactor 210. Each zone will have approximately the same volume and thesame fluid velocity. As an example, a reactor for 1 million tons (102000tonnes) per year of bitumen with two sections, each section having aneffective length of 15 meters, would have an internal diameter of about1 meter.

The lower part of the reaction zone has an internal vortex Norway-typeentrainment separator 258 which can separate any solid particles ofcoke, ash or carbon entrained with the resultant fluid mixture. Thesolid particles are removed as stream 260 and then further processed ordisposed of. A stream 262 of resultant fluid mixture (with solidparticles removed) is cooled in a heat exchanger 240 to produce a stream264 at near ambient temperature, e.g. from about 35° C. to about 50° C.Stream 264, a two phase liquid/gas mixture, is reduced in pressure overvalve 266 to produce a product stream 268 at about 50 bar which is thenseparated in a phase separator system 270 into a gaseous stream 272(predominantly methane and some C₂ hydrocarbons, hydrogen and carbonmonoxide) and some liquid phases 274, 276 and 278, i.e. hydrocarbonswith a density lower than water (stream 274), water (stream 276) andhydrocarbons with a density higher than water (stream 278).

All these product streams can be treated in a conventional componentseparation train 280. A typical separation might be a methane stream282; a fuel gas stream 284 which also contains all the CO₂ produced; aBTX (benzene/toluene/xylene) fraction 286; and a light and heavy oilfraction 288.

The heat released by cooling the product stream 262 in heat exchanger240 is greater than that required for heating the 300 bar water feedstream 238 and, therefore, the process includes a steam heating cycle toprovide heat balance. The excess heat is used to heat a stream 290 ofwater at a pressure of 150 bar delivered from a condensate pump 292 toproduce a stream 294 of superheated steam at about 793K. Stream 294 isdivided into two streams, 296 and 298. Stream 296 is used to generatepower in a condensing steam turbine 300 and 302, producing recyclestream 304. Stream 298 is further divided to produce streams 224 and 254which are used respectively to pre-heat the hydrocarbon feedstock inheat exchanger 222 and to pre-heat the oxygen in heat exchanger 252,thereby producing recycle streams 306 and 308. Recycle stream 304, 306and 308 are recycled to the condensate pump 292.

When any part of the reactor system becomes blocked by deposits of solidcoke or soot on internal surfaces, the deposits are burned away using aflow of oxygen dissolved in SCW. In this connection, the flow of stream216 of bitumen feedstock is stopped and hydrocarbon compounds are purgedfrom the system by a flow of SCW alone. Valve 310 is then opened andpre-heated oxygen gas is mixed with the SCW feed stream 242 via stream312. The oxygen/water mixture burns off any coke or soot deposits andcleans the internal components of the reactor. Excessive temperaturesare prevented by carefully controlling the amount of oxygen gasdelivered to the reactor.

EXAMPLE

The performance of a bitumen conversion process according to the presentinvention using the laboratory scale reactor depicted in FIG. 1 has beenmeasured over six test runs with varying ratios of water, bitumen andoxygen.

The reactor has an internal diameter of 28 mm, a higher temperaturereaction zone length of 170 mm, and a three stage umbrella mixer andoxygen injection system. The laboratory reactor was fitted with externalheating elements to ensure stable operation at the defined operatingtemperatures.

The feedstock considered was bitumen derived from oil vacuumdistillation with a bottom column temperature of 870K. The formula ofthe bitumen used was C₁H_(1.43)S_(0.015).

The reaction conditions for each run and the identity and proportions ofthe products are reproduced in Table 1.

TABLE 1 TEST 1 2 3 4 5 6 T_(M)(K) wall 724 [~774] 714 [~764] 706 [~756]690 [~740] 673 [~723] 702 [~752] [~fluid] T_(R)(K) wall 844 [~894] 826[~876] 875 [~925] 879 [~929] 875 [~925]  963 [~1013] [~fluid] P (bar)350 350 350 300 300 300 G_(W) (mg/s) 150 50 100 100 100 100 G_(T) (mg/s)27 28 84 114 54 97 G_(O2) (mg/s) 26 17 21 17 35 20 t_(M) (s) 48 165 9380 133 110 t_(R) (s) 32 99 44 37 37 33 t_(H) (s) 2.8 3.2 3.6 4.9 6.7 2.0H₂ (%) 0.02 0.08 0.23 0.07 0.31 0.30 CH₄ (%) 5.9 12.0 29 26 28 35 C₂H₆(%) 3.0 7.6 4.9 9.7 3.6 5.8 C₆H₆ (%) 7.1 15.9 23 22 25 24 C₇H₈ (%) 6.211.4 6.6 11.6 3.3 8.8 C₈H₁₀ (%) 3.6 9.0 1.54 3.3 0.45 2.8 C₉H₁₂ (%) 0.552.15 0.24 0.24 0.05 0.28 C₁₀H₁₄ (%) 0 0.51 0.03 0.24 0 0.13 C₁₀H₈ (%)0.34 0.59 0.74 1.62 1.54 1.68 CO (%) 4.1 2.3 2.3 0.9 4.9 3.1 CO₂ (%) 5028.4 17.6 3.4 33 4.4 (H₂O)_(f) (%) 18 3 −25 6 −9 7.2 H₂S (%) 0 0.54 1.072.7 2.0 1.84 C₄H₄S (%) 0 0 0.64 0.01 0.19 0.44 C₅H₅S (%) 0 0.52 0.270.17 0 0.53 Σ C_(x)H_(y) (%) 51 16 10 9 9 6.9 R_(S) (%) 13.6 5 6 5 9 1.6Coke (%) 9.6 12.6 10.7 10.0 12.9 10.7 BTX (%) 16.9 36.3 31 36.6 29 35.6“T_(M)” is temperature of the reactor wall in the mixing zone; “T_(R)”is the temperature of the reactor wall in the higher temperaturereaction zone; “P” is the pressure; “G_(W)” is the flow rate for water“G_(T)” is the flowrate for the bitumen (tar); “G_(O2)” is the flowratefor oxygen; “t_(M)” is the residence time in the mixing section; “t_(R)”is the residence time in the reaction zone; and “t_(H)” is the residencetime in the outlet pipe;

It is important to note that the temperature of the fluid inside thereactor is more than the temperature of the reactor wall byapproximately 50K. The approximate fluid temperatures are given inparenthesis.

The mass percentage of combustion products is normalized to the bitumeninput decreased by the combusted bitumen. In addition, the masspercentage of carbon monoxide and carbon dioxide shows only thecontained carbon quantity.

The difference in water mass flow at the reactor outlet compared to theinlet is (H₂O)_(f). If this figure is negative, more water moleculesdissociate in the reactor than are formed from bitumen combustion.

R_(s) is a high boiling point oil fraction. The coke residue has anapproximate formula CH_(0.5).

The results clearly indicate that substantial quantities of lighter,more valuable, hydrocarbon compounds such as methane; ethane; benzene;toluene; and xylene may be produced efficiently, in good yield and withreduced coke formation, directly from heavy, low grade hydrocarbonfeedstock such as bitumen using the two stage heating process of thepresent invention with internal combustion heating to raise thetemperature between the two stages. The results show that a significantdegree of hydrogenation has occurred due to dissociation of watermolecules.

The results demonstrate that the maximum yield of valuable products frombitumen conversion occurs at a temperature in the range 925K to 1025Kwhile the initial process of tar dissolution occurs at a temperature ofno more than 775K. It has also been shown that conversion rates at 925Kare rapid.

The process can be used to treat heavy hydrocarbon feedstocks to producea natural gas substitute; BTX; liquid oil fractions; and a cokefraction. The capital and running costs are typically far less than foran equivalent process involving gasification and Fischer-Tropsch liquidhydrocarbon synthesis. In addition, oxygen consumption is typically muchlower (only about 30 wt %) than for a conventional high temperaturegasification.

It will be appreciated that the invention is not restricted to thedetails described above with reference to the preferred embodiments butthat numerous modifications and variations can be made without departingfrom the spirit or scope of the invention as defined in the followingclaims.

1. A reactor system for converting heavy hydrocarbon feedstock intoconversion products comprising lower molecular weight hydrocarboncompounds, said reactor system comprising: a source of SCW; a mixingzone for mixing heavy hydrocarbon feedstock and SCW to form a fluidreaction mixture at a first temperature up to about 775K; a feedingsystem for feeding SCW from said source and feedstock into said mixingzone; a heating system for heating said fluid reaction mixture from saidfirst temperature to a second temperature from about 870K to about1075K; a higher temperature reaction zone for maintaining said fluidreaction mixture at said second temperature for sufficient time to forma resultant fluid mixture containing said conversion products, saidreaction zone being in fluid flow communication with said mixing zone;and an outlet system for removing said resultant fluid mixture.
 2. Areactor system according to claim 1 wherein said heating system is forproviding heat internally within the reactor system.
 3. A reactor systemaccording to claim 1 wherein said heating system comprises an oxygeninlet system for feeding oxygen-containing gas into said fluid reactionmixture.
 4. A reactor system according to claim 3 wherein said oxygeninlet system comprises a device for creating turbulence in a flow offluid reaction mixture for facilitating mixing of oxygen with said fluidreaction mixture.
 5. A reactor system according to claim 4 wherein saiddevice comprises at least one umbrella, the or each umbrella having atleast one outlet to feed oxygen-containing gas from under the umbrellatowards the periphery thereof.
 6. A reactor system according to claim 1wherein said outlet system comprises a separator for separatingentrained solid material from said resultant fluid mixture.
 7. A reactorsystem according to claim 1 comprising internal components made from ametal selected from the group consisting of titanium and copper andalloys thereof.
 8. A reactor system according to claim 1 comprising aplurality of concentric shells in the mixing zone to increase fluidvelocity for a given residence time.